Fig. 1

Method of quantification of tumour volume: a pelvic axial section of MR images depicting an anal canal tumour contoured in blue (arrows); b sequential contours rendered to create 3D representation of the tumour, demonstrating its irregular and complex shape; and c estimation of volume using orthogonal tumour size measurements under the assumption that the tumour volume approximates an ellipsoid. d estimation of volume using orthogonal tumour size measurements under the assumption that the tumour volume approximates an elliptical cylinder. Figures (a) and (b) were created using World-Match (inhouse written software). Figures (c) and (d) were created using Microsoft Office Powerpoint